Coated rubber stopper and process for preparing same



Patented Sept. 15, 1953 COATED RUBBER STOPPER AND PROCESS- FOR PREPARINGSAME Robert R. Umbdenstock, Brooklyn, N. Y., assignor to Chas. Pfizer &Co., Inc., New York, N. Y., a

corporation of Delaware No Drawing. Application September 15, 1949,Serial No. 115,957

2 Claims. (Cl. 226-89) This invention relates to a rubber stopper havingimproved properties which is adapted for use in machines forautomatically and mechanically stoppering vials or bottles. Inparticular, th1s invention relates to rubber stoppers having improvedproperties and which are adapted for use in packaging certain drugs andtherapeutic materials in bottles or vials under sterile conditlons.

In the past considerable difficulty has been encountered in theoperation of automatic stoppering machines using sterile, dry stoppers.After sterilization, the stoppers tend to adhere to each other in massespreventing proper feeding, jamming the machines, and causing expensivedelays in operation. Once the stoppers have passed from the feed hopperinto that section of the machine leading to the mechanism which insertsthem into the vials or bottles, they continue to cause difficulty. Theydo not roll or slide readily over the metal guiding surfaces, but rathertend to adhere to them instead of moving into the section of the machinewhich positions the stoppers just prior to insertion. Even momentaryadherence to the metal surfaces causes difficulty. Thus, it can be seenthat any method of preventing such adherence of stoppers both to oneanother and to the metal surfaces of machines in which they are utilizedis of great importance, and constitutes a valuable contribution to theart.

Various methods have been resorted to in order to overcome thesedifllculties. Rubber stoppers have been washed, sterilized and dried ina variety of manners but with little improvement in the propertiesneeded to provide a trouble-free operation in the automatic machines.Paraffin has been incorporated in rubber stoppers during theirmanufacture in such a manner that a surface coating slowly forms. Thisassists in making the stoppers free flowing, but there is a markedtendency for flakes of parafiin to become detached from the stoppers,particularly when a hypodermic needle is passed through the stopper in avial in order to withdraw a solution therefrom. This is particularlyundesirable when the solution is to be used for parenteraladministration.

Lubrication of the metal surfaces of the machines over which the rubberstoppers must roll or slide with such materials as castor oil or mineraloil makes a temporary improvement in this operation, but it does notprevent the adherence of the stoppers to one another. In addition,contact of the rubber stoppers with the lubricated surfaces duringcontinued operation of the machine soon removes the lubricants.

It has now been found that an improved rubber stopper which is suitablefor use as a bottle or vial closure and which is admirably adapted foruse in automatic stoppering machines without encountering theabove-mentioned disadvantages can be prepared by coating the stopperwith a thin film of a high boiling (that is, essentially non-volatile atnormal temperature and atmospheric pressure) rubber lubricant, liquid atroom temperature, which is stable to steam at 20 lbs. pressure for atleast /2 hour and which has a viscosity of from to 500 centistokes atroom temperature. Rubber stoppers so coated. can be sterilized and driedin the customary manner. The sterile stoppers may then be fed into themachine used in inserting the stoppers in vials or bottles. The stoppersdo not adhere to one another, they do not obstruct the mechanism forfeeding them from the hopper into the operating section of the machine.They do not adhere to the metal surfaces of the machine, but ratherslide or roll readily into position where they are picked up andinserted in the mouth of the bottle or vial. No jamming of the machinesby the stoppers involving costly delays is encountered. In addition tothe above advantages the stoppers prepared by the disclosed process maybe inserted into bottles and vials with much greater ease than is thecase with untreated, sterilized and dried stoppers. The pressurerequired to insert the treated stoppers is less, and there is lesstendency for them to pop out once inserted. This is true no matter whatmachine or method is used for placing the stoppers in the mouth of thebottle or vial.

Rubber stoppers which may be used in the 7 process of this inventionconsist of natural rubber compounded in the usual manner, reclaimedrubber or synthetic rubber, e. g. neoprene. The treatment may be appliedto rubber stoppers of various sizes, operating successfully with largeor small stoppers. The lubricants which may be used in this inventioninclude the silicone oils. The silicone oils are mixtures of methylpolysiloxanes of various molecular weights and vary in viscosity. Iprefer to use a silicone oil having a viscosity of about centistokes,but those of somewhat higher or lower viscosity, that is, from 50 to 500centistokes are operable. In addition certain vegetable oils such assesame or peanut oil which are stable to sterilization and possesssuitable viscosity and low vapor pressure can be used. Certain esters,such as tributyl citrate and tributyl phthalate also possess suitableproperties for use in this invention.

In a preferred method of applying the thin film of lubricant to therubber stoppers for use in the automatic stoppering machine a siliconeoil having a viscosity of from 50 to 500 centistokesis dissolved in asolvent, for example chloroform or carbon tetrachloride, and thestoppers are dipped in the lubricant and are drained, dried andsterilized. The concentration of silicone-oil in the solvent may varyconsiderably.- Thus, a solution of from 0.1% to 5% of silicone oil in asolvent may be used. It is preferred, however, to use a solutioncontaining from 0.2 to 1.5% of silicone oil. Other lubricants in thesame concentrations in suitable solvents. can be similarly employed forcoating the stoppers.

The manner of application of the selectedlubricant can be variedconsiderably. The stoppers can be dipped directly in the lubricant andthe excess removed. This method is not recommended, however, since ittends to leave excessive amounts of the liquidon the surface of thestopper. The lubricating liquid can also be applied to the stoppers bysubjecting them to, a fine spray of the liquid in a device suitable foragitating the stoppers so that they are coated evenly on all surfaces.The silicone oils may be applied in the form of an emulsion in water,such as Silicone Emulsion 35A (a stable emulsion of a silicone oil inwater, manufactured by the Dow- Corning' Corporation).

The selectedlubricant can be applied batchwise as by agitation in asuitable vessel or it may be applied in a continuous manner, as bypassage of the stoppers on a continuous conveyance through a zone inwhich the lubricant is applied in the form of the pure liquid, asolution, or a spray of either of these.

Rather than apply the silicone oils as such to the rubber stoppers, itis possible to form a suitable lubricating coating of a polymericsilicone on the surface of the rubber by exposing the latter to aprecursor for the silicones. Thus, if rubber stoppers, bearing a thinfilm of water normally present on suchsuriaces, are exposed to thevapors of such a product as Dri Film (a mixture of methylchlorosilanesmanufactured by General Electric Corp.) for suff cient time a film ofthe silicone will be formed by reaction with water. Anotherjmaterialsuitable for use in such treatment is dimethyl-dichlorosilanemanufactured by the Dow-Corning Corporation. The product of thesevarious methods of treatment is a rubber stopper which may be sterilizedwith steam in the usual manner, dried and is then suitable foruse inautomatic bottle stoppering machines of various types. One ,such deviceis the automatic vial stoppering machine manufactured by the AfotexProducts Company of New Brunswick, New Jersey. I

The following example is given by way of illustration and is notintended to limit in any way the scope or spirit of the invention.

Example A. batch of approximately one hundred red, virgin rubberstoppers (standard size to fit 20 cc. penicillin bottles) was placed ina beaker and covered with a 1.5% solutionof Dow-Corning Corporation 100centistokes silicone oil in chloroform. After agitating the stoppers fora short time, the solution wasremoved from the beaker and the stopperswere allowed to drain. The coated stoppers were then placed in a coveredmetal tray in a clinical autoclave and sterilized for one-half hour at20-pounds per square inch steam pressure. The tray was then placed in adryer where they were subjected to a temperature of 108 F. for fourhours. Inspection of the stoppers showed them to be perfectlyfree-flowing adhering .neither .to one another nor to any smooth, vslanted surface. The stoppers were placed in the hopper of an automaticvial stopperingmachine (that-of the Afotex Products Company) and themachine was started. The stoppers fed faultlessly from the hopper intothe slotted annular ring of the machine, down the grooved chute to thelower end where they were picked-up by the vacuum operated head whichinserted them in the glass bottles. There was no adhesion of thestoppers in the hopper; there was no adhesion to the metal walls of thehopper, to those of the annular ring or to those of the chute. Thestoppers fed steadilyand as rapidly as they were required to the pointat which they were picked up for insertion. There was no jamming of. themachine and no shut-downs as had been encountered with stoppers nottreated by the process of this invention.

This invention is not restricted to natural, reclaimed or syntheticrubber stoppers, but maybe applied to any type of bottle or vial closurewhich because of its composition and the manner in which it must behandled in automatic stoppering machines causes difiiculty due toadhesion to one another or to parts of the machine.

As many apparently widely different embodiments of this invention may bemade without departing from the spirit and scope hereof, it is to beunderstood that this invention is not limited to the specificembodiments hereof, except as defined in the appended claims.

I claim:

1. A rubber stopper suitable for use as a closure for pharmaceuticalcontainers, and particularly adapted for use in conjunction, with anautomatic stoppering' machine, which stopper is coated with a thin filmof a silicone oil having a viscosity of from 50 to 500 centistokes atroom temperature and is heat-sterilized.

2. A process for stoppering pharmaceutical containers which comprisescoating rubber stop pers with a thin film of a silicone oil, sterilizingthe-coated stopperwith steam at elevated pressure, drying the sterilizedstoppers and inserting the same under aseptic conditions in the mouthsof said pharmaceutical containers.

ROBERT R. UMBDENSTOCK.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 65,533 Bishop June 11, 1867 726,629 Brown Apr. 28,1903 811,876Schroeder Feb. '6, 1906 2,386,466 Hyde Oct. 9, 1945 2,442,059 SaffordMay 25, 1948 2,470,772 Haas May 24,1949 2,471,224 Loughborough May 24,1949 2,474,704 lfhayer June 28, 1949 2,494,920 Warrick Jan. 17, 19502,573,637 Bender Oct. 30, 1951

2. A PROCESS FOR STOPPERING PHARMACEUTICAL CONTAINERS WHICH COMPRISESCOATING RUBBER STOPPERS WITH A THIN FILM OF A SILICONE OIL, STERILIZINGTHE COATED STOPPER WITH STEAM AT ELEVATED PRESSURE, DRYING THESTERILIZED STOPPERS AND INSERTING THE SAME UNDER ASEPTIC CONDITIONS INTHE MOUTHS OF SAID PHARMACEUTICAL CONTAINERS.